I found this book extremely useful, not only in explaining, in depth, how to get the best out of the Nikon D80, but also in demystifying much of the terminology that surrounds digital photography and photography in general.
If I were thinking about buying the D80 reading this book first would help in the making of the decision as it explains where how the internal "guts" of the D80 work in comparison to other dSLRs.
If there is a downside to the book it is that as a photographic book, many of the photos of the camera showing controls could be a lot clearer. (Maybe they didn't use a D80 to take them!) Perhaps colour would be good, but then I suppose the price would be higher.
All in all I would not hesitate to recommend this book to anyone with or contemplating the Nikon D80.